Acoustics – Sound-modifying means – Housing or enclosure
Patent
1996-11-26
1998-09-08
Dang, Khanh
Acoustics
Sound-modifying means
Housing or enclosure
181202, 181204, 181208, G10K 1104
Patent
active
058047751
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lightweight stiff acoustic enclosures.
2. Discussion of Prior Art
Noise generated by machinery may be transmitted to the surrounding environment by either structural or airborne paths. The structural paths comprise mounts, pipework or other mechanical connections. Once suitable vibration isolators have been attached to the structural paths, the airborne paths become the most significant route for noise transmission.
At present, the amount of noise transmitted by airborne paths is reduced with the use of acoustic enclosures. The performance of an acoustic enclosure is controlled by three aspects: the internal acoustic absorption; the sound transmission through the wall of the enclosure; and the mechanical links between the machine and the enclosure.
Internal acoustic absorption can be attained by using fibrous material for broadband absorption and Helmholtz resonators for narrow band absorption. The vibrational noise transmitted via mechanical links, such as pipework or mounts, can be isolated using vibration isolators. The sound transmission through the wall is controlled by several factors, mass per unit area being the most significant.
As a result, the relative mass of enclosures is invariably heavy, the weight of the enclosure often being in the same order of magnitude as the machinery itself in order to provide the required performance. The best performance of these types of enclosures is achieved at high frequencies, the performance deteriorating proportionally to frequency at low frequencies.
SUMMARY OF THE INVENTION
The object of this invention is to produce a light weight enclosure which produces significant noise reduction at low frequencies.
Accordingly, there is provided a light weight enclosure for the reduction of noise transmission for monopole, quadrapole and higher order noise sources via airborne paths at frequencies lower than the approximate ring frequency of the enclosure comprising an approximately spherical shaped enclosure which is made from stiff materials to reduce the amount of stretching of the enclosure wall and substantially encases the noise source, all structural paths between the enclosure and the noise source comprising vibration isolation.
It is preferable that all structural paths between the enclosure and the object to which it is mounted comprise vibration isolation.
The vibration isolation in the structural paths between the noise source and the enclosure ensures that the noise transmission from the noise source to the enclosure is only through the air within the enclosure. The vibration isolation prevents the vibrations of the noise source from being passed to the enclosure which, being stiff, would radiate the noise particularly well. The vibration isolation in the structural paths between the enclosure and the object on which it is mounted also helps prevent unwanted vibrations being passed to the enclosure.
Structural paths include mounts pipework or other mechanical connections.
At high frequencies, noise transmission through the walls of an enclosure is dependent on the amount of transversal flexing of the walls. The amount of transversal flexing is dependent on the mass per unit area of the wall. Therefore, the amount of transversal flexing can be reduced by raising the mass per unit area of the enclosure wall. However, at lower frequencies, the inventor has found that the amount of noise transmission through the wall is also dependent on the stretching of the walls of the enclosure. Therefore, by reducing the amount of stretching, the amount of noise transmission at low frequencies can be reduced. This is achieved by making the enclosure as stiff as possible.
Because noise transmission due to the stretching of the walls of an enclosure is dependent on the stiffness and not on the mass, the thickness of the enclosure wall can be made to be relatively thin. However, if desired, the enclosure could still be made to have a high mass per unit area as well as being stiff. By do
REFERENCES:
patent: 4190131 (1980-02-01), Robinson
patent: 4345882 (1982-08-01), Saito et al.
patent: 4384635 (1983-05-01), Lowery
patent: 4729723 (1988-03-01), Outzen
patent: 4834625 (1989-05-01), Grant
patent: 5272285 (1993-12-01), Miller
patent: 5487648 (1996-01-01), Alfano et al.
patent: 5538404 (1996-07-01), DiFlora et al.
patent: 5588810 (1996-12-01), DiFlora et al.
Dang Khanh
The Secretary of State for Defence in Her Britannic Majesty's Go
LandOfFree
Light weight shell acoustic enclosure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light weight shell acoustic enclosure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light weight shell acoustic enclosure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1283652